CBQE-1220 Remove cluster topology change for warmup test

Change-Id: I89c8ef88ad97e617742c65d5bdcdf040d1f0009f
Reviewed-on: http://review.couchbase.org/26040
Reviewed-by: Chisheng Hong <chisheng@couchbase.com>
Tested-by: Chisheng Hong <chisheng@couchbase.com>